net: renesas: rswitch: add offloading for L2 switching

net: renesas: rswitch: add offloading for L2 switching

Add hardware offloading for L2 switching on R-Car S4.

On S4 brdev is limited to one per-device (not per port). Reasoning
is that hw L2 forwarding support lacks any sort of source port based
filtering, which makes it unusable to offload more than one bridge
device. Either you allow hardware to forward destination MAC to a
port, or you have to send it to CPU. You can't make it forward only
if src and dst ports are in the same brdev.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Michael Dege <michael.dege@renesas.com>
Link: https://patch.msgid.link/20250901-add_l2_switching-v5-3-5f13e46860d5@renesas.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>